Angular-position measuring devices, also referred to frequently as rotary encoders, are used to measure rotational movements of a rotationally mounted machine part, particularly a shaft, over one or more revolutions. In so doing, the rotational movement is recorded incrementally or absolutely. In connection with gear racks and gear wheels or with threaded spindles, linear motions can also be measured by an angular-position measuring device. Such angular-position measuring devices are often used in conjunction with electric motors to generate a commutation signal.
Angular-position measuring devices which must satisfy comparatively high demands with regard to measuring accuracy frequently operate according to an optical measuring principle, the measuring standard often being implemented as a glass ring, for example, having an angle scaling applied on it. In this case, the angle scaling is scanned by an incident light technique or a transmitted light technique. In order to ensure high measuring accuracy, it is important for the measuring standard to be protected from contaminants. It may be particularly disadvantageous if lubricant or components thereof escape from the roller bearing and deposit on the measuring standard, especially in the area of the angle scaling. Such contaminants are often in the form of droplets, and exhibit an optical effect, similar to that of a lens. Under such circumstances, the light beams are deflected accordingly, which can lead to a faulty measurement.
European Published Patent Application No. 2 378 251 describes an angular-position measuring device which has a shaft having a groove that is connected to a hollow space for receiving lubricant.